This invention relates to a toner for electrophotographic reproduction by a dry developing process.
Copied images of electrophotography are black in general but in recent years, a reproduction machine capable of copying images in a color other than black has been introduced.
Among color-copied images, white-copied images are formed on a color copying paper, for example, on a black paper to have a striking contrast thereby providing images with visual beauty. White-copied images have a beauty different then black-copied images. White toners are constituted of pigments represented by titanium dioxide, binder resin and additives etc. When copied images are formed with white toners, hiding properties are particularly required. Hiding properties is defined as the power to hide a background such as copying paper when toners are fixed on the background. Black-copied images do not appear unclear even if the hiding properties are not so sufficient. But, white-copied images appear unclear even if white toners have hiding properties comparable to that of black toners. Conventional white toners have insufficient hiding power to form white images without showing an unclear appearance.
It is proposed to improve the hiding properties such that the content of white pigments, such as titanium dioxide, in white toners, are increased. The higher content of the pigment brings about problems such as the flying of toners or a poor resistance to the environment. It is thought that these problems result from poor dispersion properties of the pigments. The flying of toners causes fogs on copying paper and the poor environmental resistance causes the decrease of toner-charging properties. Further, alienated pigments cause poor cleaning properties.